# Assumed temperature on FMC and landing question

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A bit hazy on two topics:

-How do you exactly pick the temperature to set on  the SEL/OAT? is it always 15 + what ever the outside temperature is,  is it that simple?

-When landing with APP engaged but without the FULL auto land option (Autopilot B no engaged) it is my understanding that you get guided until the runway but you need to land yourself, am I correct here? if so,  what is the decision height at which you take control of the plane? is it decided by the FMC telling you when to take over (how?) or is up to the pilot to decide based on visibility and outside conditions? and what you do manually do,  disengage auto pilot and auto speed?

thanks

Andrea De Biase

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The assumed temperature will be arrived at through a calculation. Runway length plays a part here as well as obstacle clearance in addition to aircraft weight, wind direction and OAT. A tool such as TOPCAT can do the calculation for you.

OAT should be the actual OAT, so if you calculate an assumed temperature takeoff of 50c and the OAT is 20c  the FMC input should be 50/20

When conducting a normal (non-autoland) landing, you should disengage the A/P and A/T somewhere between 1000 and 1500 feet above the airport elevation. Different airlines will have different procedures, but you should be in landing configuration (flaps and gear down) and in a stabilised approach with regard to descent path and speed. The height at which this takes place will be decided by the airline's SOP, you will get no guidance from the aircraft itself.

Decision HEIGHT is a term that is usually used for autolands as it refers to radio height above the ground. When conducting a Cat 1 ILS or VOR/NDB (manual landing) you will be using decision ALTITUDE which is barometric altitude. The two numbers will vary widely depending on the altitude of the airport. But note that DH or DA are the point at which the pilot must decide to continue the landing if the visual requirements are met (seeing the runway) or not continuing the landing (going around) if the visual requirements are not met. These heights/altitudes are published on the approach charts for each individual runway.  DH or DA are not where the pilot takes manual control of the aircraft, that must happen before.

Different aircraft have different recommendations for use of A/P and A/T. The 737 is one where Boeing recommends the A/T should be disengaged when the A/P is disengaged on approach.

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When conducting a normal (non-autoland) landing, you should disengage the A/P and A/T somewhere between 1000 and 1500 feet above the airport elevation. Different airlines will have different procedures, but you should be in landing configuration (flaps and gear down) and in a stabilised approach with regard to descent path and speed. The height at which this takes place will be decided by the airline's SOP, you will get no guidance from the aircraft itself.

I clearly misused the proper verbiage and got from your reply what i needed plus more. Thank you

Andrea De Biase

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When landing with APP engaged but without the FULL auto land option (Autopilot B no engaged) it is my understanding that you get guided until the runway but you need to land yourself, am I correct here? if so, what is the decision height at which you take control of the plane? is it decided by the FMC telling you when to take over (how?) or is up to the pilot to decide based on visibility and outside conditions? and what you do manually do, disengage auto pilot and auto speed?

thanks

Andrea De Biase

MUH for single chanel A/P landing is 158ft

Decision Altitude/Height (DA/H)

A specified altitude or height in the precision approach, at which, a missed approach must be initiated if the required visual reference to continue the approach has not being established. Decision altitude is referenced to MSL and the decision height is referenced to the threshold elevation.

Minimum Descent Altitude/Height (MDA/H)

A specified altitude or height in a non precision approach or circling approach below which descent may

not be made without visual reference.

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